Hydrofluoric acid resistant packing material



March 11, 1947. J, D. CovlNGTQN 2,417,351

HYDROFLUORIG ACID RESISTANT PACKING MATERIAL Filed July 7, 1944 TMHMMENQ@ NSU @su ZQNRU NN@ Patented Mar. 11, 1947 HYDROFLUORIC ACIDRESISTANT PACKING MATERIAL James D. Covington, Dallas, Tex., assignor,by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, NewYork, N. Y., a corporation of New York Application July 7, 1944, SerialNo. 543,855

2 Claims.

This invention relates to packing materials, and particularly to packingmaterials employed in the control units of systems or processesutilizing hydrouoric acid, particularly to processes for thecondensation of hydrocarbons, such as the alkylation f isoparaffins witholens, the polymerization of olens, the alkylation of aromatichydrocarbons with olefins and the like.

-A typical application of my invention is its use in a commercialalkylation process, 'such as the alkylation of isoparaflins such asisobutane with oleiins such as the butenes. The invention will beillustrated as applied to an alkylation process of this type. It is tobe understood, however, that the principles of my invention areapplicable to any process or system wherein essentially anhydroushydrogen iiuoride is utilized as a catalyst or other treating agentand/or wherein control of the flow of this acid or its agitation arerequired.

Hydrouoric acid exerts a strong corrosive action on many 0f thematerials normally used in the construction of reiinery equipment. Also,the acid is highly toxic and is therefore a potentially hazardouschemical. For these reasons the use of hydrouoric acid asl an alkylationcatalyst has introduced new problems in design, construction andoperation of refinery equipment.

A particularly troublesome problem encountered in HF alkylation plantshas been the frequent occurrence of leaks in circulating pumps andcontrol valves and the like through which hydrofluoric acid, or mixturesof hydrofluoric acid and hydrocarbonsare conducted in the process. Theseleaks are caused mainly by deterioration of the packing used in theseunits due to the action of the hydroiiuoric acid, although infrequently,corrosion of the metal parts of such units, after prolonged exposure tothe acid, is a contributing factor. These leaks are not only troublesomefrom an operational standpoint but they constitute a serious hazard topersonnel because of the high toxicity of the acid.

It is an object of my invention to provide a novel compacted packing andlubricating material for use in flow control units, such as pumps,valves and the like which are employed in systems carrying hydrofluoricacid, said packing material being highly resistant to the action ofhydrouoric acid. whereby the occurrence of costly and hazardous leaks,due to packing failure in such control units is substantially minimized.

I have discovered that when units such as pumps and valves, which handlehydroiiuoric acid or mixtures containing hydrouoric acid such as in thealkylation of isobutane with butenes,

are packed with a packing material comprising talc instead of theconventional packing materials the operating period during which noleakage will occur in such units is greatly increased.

In order that a full understanding of the invention and the advantagesto be derived from its use may be had, reference is made to theaccompanying drawing which is a iiow diagram of a conventional processfor producing alkylated hydrocarbons from isobutanes and butenes utiliz-'ing hydrogen fluoride as a catalyst.

In the drawing there is shown a reaction circuit I into which butenefeed stock is admitted through line 2 -tted with valve 3. isobutane feedstock is fed to the reaction circuit through line 4 fitted with valve 5.Essentially anhydrous hydrouoric acid catalyst is delivered to thereaction circuit through line 6 provided with valve I by way of line 8.A circulating pump II) cir` culates the reactants and the hydrofluoricacid continuously around the reaction circuit. A cooler II is providedin order to maintain the reactants at the desired reaction temperature.The reactants may be by-passed through the cooler II in any desiredproportion by means of ow regulation valve I2. Material is continuouslywithdrawn from the circulating mixture through line I3 provided withvalve I4 to separator I5 where gravity separation of hydrofluoric acidfrom reacted and unreacted hydrocarbons occurs, forming an acid phaseand a hydrocarbon phase. The heavier acid phase settles to the bottom ofthe separator I5 and is withdrawn through line 8 provided with valve I6and recycled to reaction circuit I by means of a pump 20. Thehydrocarbon phase is withdrawn from the top of separator I5 through line2|' provided with valve 22 and passed to fractionating column 23provided with reboiler 2li.v Small amounts of hydrouoric acid carriedover in the eiliuent stream from the separator I5 may be removed fromthe process at this point by treatment in a suitable alkaline absorberor by means of a hydroiiuoric acid stripper (not shown). Liquid alkylateproduct is withdrawn from the bottom of fractionator 23 through line 25fitted with valve 26 while the lighter components of the reactedmixture, comprising unreacted isobutane with small amounts of n-butaneand lighter gases such as propane, ethane, etc., formed in the reactioncircuit are taken o overhead in line 21. In line 21 the isobutane andnormal butane-containing fraction is conducted to fractionator 28 inwhich the isobutane is separated and recycled to reaction circuit I byway of line 29 provided with compresser 30, cooler 3| and valve 32.Normal butane is withdrawn from fractionator 28 in line 33 fitted withvalve 34, while the gases lighter than isobutane are vented through line35.

In the operation of the hydrofluoric acid'alkylation process justdescribed trouble has been encountered due to the frequent occurrence of`leaks in the hydrofluoric acid recycle stream pump 20 and in thecirculating pump i0. Leaks were also encountered, though they were lessfrequent, in control valves 1, I4' and I6. All of these leaks were theresult of deterioration of the conven` tional packing used in theseunits. The life of the packing material in the circulating pumps underconditions of continuous operation was only a few hours on the averageand rarely exceeded a day after which time leakage occurred andrepacking was necessary. However, when in accordance with my invention apacking composition comprising talcumpowder was employed in these umtsleakage was prevented for periods' as long as from 3 to 5 weeks. underconditions of continuous operation. This represents about a thirtyfoldincrease in the length of the packing life. The fact that talc is soeiective for this purpose is surprising since it is essentially asilicious material (MgO.4SiO2.H2O) and there` fore would be expected tobe attacked readily by hydrofluoric acid. Whether a reaction does occurbetween the talc and the hydrogen uoride to produce a substance whichaffords the talc its eectiveness as a packing in the presence ofhydrogen fluoride is not known to me, the evident fact being. that'it isso eiective.

In order to reduce friction and a'ord a lubricating quality to the talc,I generally mix the talc with ilake graphite. I have found that bestresults are obtained by using a mi-xture of talc and graphite containingfrom about to about 25l percent by weight of graphite although mixturescontaining as high as 50 percent may be employed.

Though I have described and illustrated my in-` vention inconnectionwith an alkylation process, it should be understood that theprinciple of the invention is equally applicable to other hydrofluoricacid processes or to systems carrying hydrouoric acid or mixturesthereof in which circulating pumps, agitators and stirrers having packedshafts, bearings, etc., are exposed to hydrogen fluoride.

pacted packing and lubricating mass consisting of an intimate mixture oftalc and ilake graphite,

said mass characterized by being highly resistant to the action ofhydrogen uoride and the talc being present in an amount from about "I5kto about 90 per cent of the total weight of the mixture.

2. As a new article of manufacture a compacted packing and lubricatingmass characterized by being highly resistant to the action of hydrogenfluoride consisting of an intimate mixture of talc and flake graphite inwhich the talc comprises from to about,90% by weight of the mixture.

JAMES D. COVINGTON.

REFERENCESy CITED The following references are of record in the le ofthis patent:

UNITED' sTATEs PATENTS Number Name Date 1,409,276 Benjamin Mar.- 14,1922- 1,363,563 Calts Dec. 28, 1920 2,322,800 Frey June 29, 19432,363,597 Jones Nov. 28, 1944 2,357,753 Matuszak Sept. 5, 1944 FOREIGNPATENTS Number Country- Date 325,566 British Feb. 14, 1930 OTHERREFERENCES National Pet. News, Tech. Soc., June 2, 1943,

(Patent Office Library.) National Pet. News, Tech. Soc., Mar. 1, 1944,

Vpp. R-146, R-148, R-150, R-151, Elf-1.54, R455.

Chem. Abs., v01. 26, page 446.1, Aug. 2o, 1932, 252-29. (Copy in Div.64.)

